Current epoxy resins and many other plastics are often prepared using bisphenols, the most common of which is bisphenol A. However, bisphenol A exhibits hormone-like properties that have raised concerns about its suitability in consumer products and food containers. Bisphenol A is thought to be an endocrine disruptor which can mimic estrogen and may lead to negative health effects. More specifically, Bisphenol A closely mimics the structure and function of the hormone estradiol with the ability to bind to and activate the same estrogen receptor as the natural hormone. Since 2008, several governments have questioned its safety, and a 2010 report from the United States Food and Drug Administration (FDA) warned of possible hazards to fetuses, infants, and young children.
Industry has responded to criticism of BPA by creating “BPA-free” products, which are made from plastic containing a compound called bisphenol S (BPS). BPS, which shares a similar structure and versatility to BPA, is now being used in everything from currency to thermal receipt paper, and widespread human exposure to BPS was confirmed in a 2012 analysis of urine samples taken in the U.S., Japan, China and five other Asian countries. However, BPS, like BPA, shares similar problems to BPA in that it has been found to be a hormone disruptor even at extremely low levels of exposure.
A number of investigators have synthesized degradable polymers made from tyrosine and other amino acids and have found that they have high biocompatibility since they are capable of degrading to biologically safe molecules. These polymers are urethanes, carbonates or iminocarbonates synthesized through cyanate based chemistry (another source of potential cytotoxicity). Gupta, A. S. & Lopina, S. T., Journal of biomaterials science 13, 1093-1104 (2002). Kohn, J. & Langer, R., Biomaterials 7, 176-182 (1986). Sarkar et al., Journal of biomedical materials research 90, 263-271 (2009). However there remains a need for bisphenol replacements that can be used as precursors for epoxy resins, and in particular epoxy resins that are safe but not readily degraded.